Aviation gasoline



Patented Ap so, 194

can

I nvm'rron cssomns Frederick T. Weiss, Normandy, Mo., and Clifford v Arbuthnot, Wood River, 1111., assignorsv to .Sheli Development @ompany, San Francisco, I, Calif a corporation of Delaware No Drawing. Application October 19, 1942, Serial No. 462,620

7 Claims.

This invention relates to fuel for spark ignition internal combustion engines and more particularly to blended aviation gasolines consisting essentially of predominantly non-aromatic aviation base stocks to which have been added minor amounts of hydrindene.

Aviation gasolines, particularly those employed in military service, must, in addition to high octane number 'as measured by the A. S. T. M. method D-614, have a high supercharge rating, that is, it must be possible to obtain with this gasoline by supercharging and certain other modifications a very high power output without the occurrence of knock in the engine. It is known that the knocking tendency of fuels can be reduced within certain limits by enriching the fuelair mixture, and that the suppression of the knocking with a given degree of enrichment varies with different fuels. The tendency of the fuel to respond to enrichment of the combustible mixture and its ability to permit high power outputs at rich mixtures without knocking is measured by the now accepted AFB-3C testing method which has been approved by the C. F. R.

Certain aromatic hydrocarbons when added in minor proportions to predominantly non-aromatic base stocks are known to be quite effective in suppressing knocking upon enriching the fuel-air mixture. while others are not.

' Inasmuch as the improvement in rich mixture response of various-blends of an carbon with a substantially non-aromatic base fuel is not proportional to the amount of the aromatic added, it was necessary, in order to evalinto the usefulness of various aromatic hydrocarbons, to first develop a method whereby the blending value of aromatic hydrocarbons with respect to their ability to improve rich mixture response of the blends could be measured. The method devised in answer to this need measures the volume of a standard alkylate gasoline which can be replaced by one volume of the aromatic hydrocarbon when substituting enough of said aromatic hydrocarbonforsaid alkylate in a blend consisting of 70% alkylate and 30% of a standard straight-run aviation base stock so as to produce a new blend of identical 86 rating containing of the aromatic. In cases where the aromatic hydrocarbon replaces more than volume for volume of alkylate. the diflerence is made up by the addition of base stock. The standard alkylate is one produced by condensing isobutone with normal butylcnc in the presence of sulfuric acid at about 50' F. Ind with dmLTEL/gal. has a rich mixture ratio: equivalent to 8 reference fuel+2.'l5

aromatic hydro-.-

octane number of 99+, as determined by either i A. S. T. M. method 357 or 614; and fuel M is straight-run gasoline. from Michigan crude having an octane number of ,1 9 /2,determined by A. S.

T. M. method 357. l e We have discovered that hydrindene (cyclotrimethylene benzene) is an aromatic hydrocarbon which has the property of greatly increasing the rich mixture response of parafllnic and/ or naphthenic aviation base stocks to which it is added. A hydrindene of 90% purity produced by reduction of indene had an ARV of 2.3.

Hydrindene has a boiling point of 350 R, which is well within the boiling range of motor fuels but is quite high for aviation gasoline requirements. Therefore in aviation gasoline the amounts of hydrindene which can be incorporated are limited. Diflerent boiling range specifications of aviation fuels impose different ceilings on the permissible amounts. Thus present-day fighting grade gasoline may contain up to 5% hydrindene. Other aviation grades may contain up to 15%. and future developments which may make the use of higher boiling aviation fuels practicable may allow even higher percentages.

' In order to realize a material benefit from the addition of the hydrindene. it is desirable, though not essential. to use not less than about 1%, and 40 preferably at least about 3%.

Because of the relatively high-boiling temperatule-of the hydrindene in relation to present aviation fuel specifications, it is desirable that base stocks to which it is added haveboiling ranges substantially below the allowable upper boiling range limits which call for maximum A. S. T. M. boiling temperatures at 90% evaporated between about 257 F. and 300 n Thus it is in general desirable to choose a base stock whose A. S. '1. M.

end boiling point is not higher than the speci- 'fled maximum boiling'point' at 90% evaporated. For example, it the-specification call for a. maximum temperatm'e of 293 F. at 90% evaporated,

. it is desirable that the. end base stock is not above about 298 1".

boiling point of the Hydrindene is available by reduction 0! indene. which in turn is a by-product of the coal tar industry.

Suitable predominantly non-aromatic aviation base stocks which may be blended with the hydrindene comprise straight-run gasoline distillates as obtained by distillation of various crudes, alkylate gasoline obtained by condensing iSObU'. tane with C3C5 olefins in the presence of sulfuric acid, hydrofluoric acid, aluminum chloride, etc., gasolines obtained by polymerization of CaC5 oleflns and hydrogenation of the resulting polymers, catalytlcally cracked gasolines of low olefin contents, etc., or blends of any of the above with minor amounts of relatively low-boiling aromatic hydrocarbons, such as benzene, toluene, xylenes, ethyl benzene, cumene, miiged alkyl benzenes as, for example, obtained by double reformquantities of aromatic amines having anti-knock propertie such as aniline, toluidine, methyl aniline, etc. Gum inhibitors and stabilizer for tetra-ethyl lead, etc., may also be present.

We claim as our invention:

1. Anaviation gasolinecontaining from about 1% up to about 15% hydrindene.

2. A fighting grade aviation gasoline containing from about 1% up to about 8%. hydrindene.

3. An aviation gasoline consisting essentially of a blend of predominantly non-aromatic aviation base stock and irom about 1% up to not more than about 15% of hydrindene.

FREDERICK T. WEISS. CLIFFORD E. ARBUTHNOT. 

